The invention relates to a feeding device, in particular for the cycled feeding of rod or tape like material in presses, cutters or the like, wherein at least one feeding roller or wheel, respectively, is driveable by means of a controllable hydromotor, and that the feeding path is advanced by a setting means and is controllable by a true value indicator which acts on a hydraulic control valve.
It is known to control the hydromotor by a servo valve which is controlled by a magnifier in such a feeding device, wherein the drive speed of the hydromotor is measured by means of a tacho-alternator and the real displacement path is measured by an incremental path measuring system and is electrically controlled by means of a nominal value comparison, while the magnifier control the servo valve. The nominal value feeding may be achieved through a direct current motor or a stepping motor. The control circuit amplification which is obtained with such an arrangement is fed through the incremental indicator and the electric control logic is relatively small, that is, one can operate exactly with such an arrangement, but due to the small control circuit amplification only correspondingly low stroke number are achievable.
In highly dynamic rapid drives, the feeding rollers must be strongly engaged so that the slippage between material and feeding rollers is kept low. However, connected therewith is the disadvantage that with different material hardness or with coated materials, for example, with a plastic coating a rolling out effect occurs within one feeding. This rolling out effect results in longitudinal errors in addition to slippage. In order to take such errors into consideration it is known not to determine the true value position from the position of a feeding roller, but by a metering wheel which runs on the rod or tape like material in accordance with one or a plurality of feeding rollers.
Electro-hydraulical rotary magnifier drives are now known with which a high dynamic rapid drive is made possible. With high dynamic stepping motors in the nominal value feeding such a high control circuit magnification can be obtained and is at this time the fastest drive for the aforementioned applications (U.S. Pat. No. 3,797,364).
The advantage of the high control circuit amplification is getting lost when using a metering wheel in conjunction with an incremental measuring system by converting mechanical measuring dimensions into electrical dimensions and reconverting during the control into a mechanical dimension for controlling the servo valve.